The compounds of formula (I) are unsaturated macrocyclic lactones of known chemical structure. They have in fact been cited as by-products or intermediate compounds in a process for the preparation of fragrant saturated macrolides such as pentadecanolide, known commercially under the tradename of EXALTOLIDE.RTM. (origin: Firmenich SA, Geneva, Switzerland), and analogues thereof [see, for example, U.S. Pat. No. 3,890,353 or J. Becker and G. Ohloff, Helv. Chim. Acta, 2889, (1971)]. According to this prior art process, an appropriate peroxide was cleaved by means of thermal or radiation energy, or yet of chemical agents, to provide a mixture containing the desired saturated lactones, as well as their unsaturated counterparts. The saturated lactones were then either separated from the mixture via the usual techniques, or obtained by hydrogenation of said mixture or of the unsaturated lactones there-contained. As it was formulated, the prior art process provided a solution to the problem of preparing EXALTOLIDE.RTM. and analogues thereof, while the corresponding unsaturated derivatives obtained simultaneously were actually undesirable products of the same process. Since the individual olfactive properties of said unsaturated lactones as such were not recognized at the time, the process comprised a systematic hydrogenation step adapted to convert said unsaturated derivatives into the desired saturated lactones. Furthermore, this hydrogenation step was in fact claimed as an essential characteristic of the prior art process.